1. Field of the Invention
In a first aspect thereof, the present invention relates to a method for manufacturing a belt structure of a green tire for vehicles.
This invention also refers to a plant for manufacturing the belt structure, a method and a plant for manufacturing a belt package of a green tire incorporating the above-mentioned belt structure, as well as a method and a plant for manufacturing a crown structure of a green tire including the above-mentioned belt package.
2. Description of the Related Art
As is known, a green tire is essentially constituted by a composite structure obtained by assembling together a plurality of semi-finished products adapted to constitute a carcass comprising at least one airproof liner, a reinforcing ply, two bead wires to which the ply edges are associated after interposition of an elastomeric filling fixed to the radially outer surface of each bead wire, a belt structure arranged as a crown around the torically shaped carcass, a tread wrapped around the belt and a pair of axially opposite sidewalls, radially extending between the bead wires and the tread.
A further layer incorporating a plurality of circumferentially oriented reinforcing cords, otherwise known as zero degree cords, may be inserted between the belt structure and the tread.
In the following description and in the subsequent claims, the term “belt structure” is used to indicate a composite structure including at least a couple of radially superposed belt strips, provided with reinforcing cords parallel to one another in each strip and inclined with respect to the cords of the adjacent strip generally in a symmetrical manner with reference to the equatorial plane of the belt structure.
In the following description and in the subsequent claims, the term “belt package” is used to indicate the assembly constituted by a belt structure and an additional radially outer layer incorporating circumferentially oriented reinforcing cords.
Finally, in the following description and in the subsequent claims, the term “crown structure” is used to indicate a composite structure constituted by a belt package and a tread in its turn arranged as a crown around the additional layer of reinforcing strips of the belt package.
In the field of tire manufacturing, one of the requirements to be satisfied is notoriously that of imparting to the finished product high quality and long lasting characteristics, achieving at the same time a high production capacity of the manufacturing plant as a whole. In this connection, a critical factor which sharply influences the quality of the finished tire is constituted by the quality of the semi-finished products which form the tire structure once they have been assembled together.
The quality of the semi-finished products is in turn linked to the production methods and to the environmental conditions in which the semi-finished products are produced and optionally stored.
According to the state of the art, in the manufacturing of the belt package of the green tire, both the belt strips and the rubber mixture ribbon (or tape) incorporating the zero degree cords forming the above-mentioned additional reinforcing layer, are wound around spools to form overlapping layers and are subsequently stored until they have to be used in the production line and assembled on an assembly drum.
A first problem connected to this type of handling of the semi-finished products is essentially linked to possible variations of the adhesion, of the chemical-physical characteristics and of the dimensional characteristics of the semi-finished products, which take place both during the storing period and during the various handling steps which such semi-finished products undergo before being used in the production line.
During the storing period in which they are kept in spools, in fact, a change of the humidity and temperature conditions of the storing environment from those considered to be optimal may lead to an unwanted variation of the rubber stickiness, generally a reduction of the same, which makes in some cases numerous layers of the semi-finished product unusable with an ensuing waste of material.
A second problem connected to the methods of handling and storing the above-mentioned semi-finished products consists in the possible appearance of undesired deformations and stresses due to the weight of material, which generally determines a compression of the radially innermost layers of material in the spool, which compression influences in turn the quality of the final product in a negative manner. In the worst cases, such compression of the layers may cause the rejection of the material which may no longer be used.
Another problem related to the above-mentioned handling methods of the semi-finished products, in particular of the belt structure, of the layer incorporating the zero degree cords and of the tread, consists in the need to carry out a series of cumbersome operations of loading and unloading of the spools in the assembling machine, which require both a continuous need for labor intervention and continuous stops, all this to the detriment of the quality of the final product and of the productivity of the plant used for manufacturing the green tire.